The location of neurons in the cat's vestibular nuclei which give rise to the main ascending and descending fiber projections is being studied by the use of a tracer (horseradish peroxidase) of retrograde axoplasmic flow. The HRP is placed around the cut ends of the axons of these projections near their termination and allowed 24 hours to travel to cells within the vestibular nuclei. Other nuclei in the caudal brainstem associated with the vestibular system are also being studied by this method. Nuclei of the vagus nerve such as the nucleus ambiguus and the retrofacial nucleus have already been studied while the nerve fiber composition of their peripheral nerve (vagus and recurrent laryngeal nerve) is presently under study. BIBLIOGRAPHIC REFERENCE: R.R. Gacek. Localization of Laryngeal Motor Neurons in the Kitten. Laryngoscope (Nov. 1975 issue).